Temporary fastening devices, often referred to as pin clamps, are frequently used in mechanical engineering and in particular in aircraft construction for preassembling the structural members constituting an aircraft, such as fuselage panels or wing panels, assembled onto frames, stringers, stiffeners, ribs and spars.
Devices known in the prior art generally include a hollow cylindrical body that is supported on a first side of the structural members being assembled, in which a rod/clamps unit, itself constituted from a threaded rod, at a first end of which two semi-clamps are fixed, equipped with retractable spoilers supported on the second side opposite the structural members being assembled. A nut is applied to the second threaded end of the rod and is supported on the posterior side of the hollow body.
The nut is therefore driven in rotation on the threaded rod by means of a screwing type assembly tool, which causes the retraction of the rod/clamps unit until the spoilers become supported on the opposite side of the structural members being assembled so as to anchor them firmly under a determined preload stress.
After the preassembly operations are complete, these devices can be removed by unscrewing the nut so that the rod/clamps unit is pushed back in the opposite direction and so as to enable the spoilers to be radially retracted to enable the device to be extracted from the hole perforated into the structural members.
Such temporary fastening devices are, for example, described in patents FR 2 513 708 or EP 336 808.
These devices are frequently used for preassembling metallic structural members, in particular made out of aluminium alloy with a mechanical strength capable of supporting, without undergoing any major damage, the high levels of local contact pressure exerted by the spoilers onto the weak bearing surfaces inherent to the concept of retractable clamps.
On modern aircraft, an increasing number of metallic structural members are being replaced by composite materials strengthened with fibres such as glass or carbon fibres. The multilayer structure of these materials makes them sensitive to delamination between layers. This form of damage, which can significantly deteriorate the mechanical strength of such materials, often occurs around a hole perforated in the composite material, in particular under high levels of local contact pressure and the sharp edges of the spoilers of the pin clamps previously described in the prior art.